Rolling lobe airspring

ABSTRACT

A rolling lobe airspring of the type embodying a tubular flexible member of substantially uniform thickness throughout its length and circumference includes a modified piston. The piston includes a recess near its end which is secured to the flexible member. The end of the flexible member lies in the piston recess. A method of assembly of such an airspring is also described.

This is a continuation of application Ser. No. 18,400 filed Mar. 8,1979, now abandoned.

The foregoing abstract is not to be taken as limiting the invention ofthis application and in order to understand the full nature and extentof the technical disclosure of this application reference must be madeto the accompanying drawings and the following detailed description.

BACKGROUND OF THE INVENTION

This invention generally relates to fluid springs such as pneumatic orairsprings, of the type used in fluid suspension systems. Moreparticularly this invention relates to fluid springs of the type inwhich a piston moves within a flexible resilient member or sleeve tocause compression and expansion of the confined fluid. Such airspringsare commonly known as reversible sleeve or rolling lobe type airspringsas distinguished from bellows type airsprings.

In a rolling lobe type airspring at least one of the elements to whichthe flexible member is secured is a generally cylindrical piston usuallymade of metal or plastic and which is employed to cause compression andexpansion of the fluid contained in the spring. When a load is appliedaxially (that is, in the lengthwise direction) of this type of springthe piston moves within the flexible member which reverses upon itselfto form a rolling lobe which rolls over the piston. The resulting changein the configuration of the spring member consequently changes thepressure of the fluid contained in the chamber. The outer surface of thepiston over which the lobe of the flexible member rolls as well as therest of the components of the airspring are carefully engineered toprovide the desired operating characteristics. Variation in the surfaceover which the rolling lobe travels during operation of the airspringresults in undesired deviations from the air spring's designcharacteristics.

In known rolling lobe airsprings, the flexible tubular member comprisesa generally cylindrical member of elastomeric material havingreinforcements therein. At least one end of the flexible membertypically is of tapering thickness upon completion of the moldingoperation. When the flexible member is secured to the piston thistapered end may extend into the working area of the piston contourcausing a noticeable and undesired change in the fine tunedcharacteristics of the airspring. Another problem with this knownairspring design is that the rolling lobe of the flexible member may inservice repeatedly roll over the tapered end portion of the flexiblemember which lies on the piston surface resulting in rubber reversion orchemical breakdown whose tacky nature may cause undesirable dirt andforeign material build-up on the piston working area. Such build-upswill change the airspring's characteristics and may reduce its servicelife.

It is an object of the invention to provide a rolling lobe airspringemploying a tubular flexible member which substantially reduces oreliminates the possibility of variation from the design characteristicsof the airspring.

It is another object of the invention to provide a tubular flexiblemember rolling lobe airspring in which the possibility of undesirablepiston build-up to the rubber reversion or chemical breakdown issubstantially reduced or eliminated.

SUMMARY OF THE INVENTION

In accordance with the present invention it has been discovered that theabove objects and advantages are accomplished by a flexible tubularmember of substantially even thickness throughout its length andcircumference which is sealed in airtight manner at its two axiallydistant ends. At least one end of the member is attached to a piston.The opposite end of the flexible member may be attached to a piston orto a plug. The piston includes a circumferential recess of a depthcorresponding approximately to the thickness of the flexible member. Therecess is located adjacent the end of the piston which is inserted inand secured to the flexible member. Preferably, the ends of the flexiblemember are secured by means of ring-shaped fittings. The piston end ofthe flexible member lies in the recess of the piston and preferablysubstantially fills the recess.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an elevational view in section showing the left half of atubular rolling lobe type airspring according to the prior art, theairspring being substantially symmetrical about its longitudinal axis;

FIG. 2 is an elevational view in section showing the right half of atubular rolling lobe type airspring according to the invention, theairspring being substantially symmetrical about its longitudinal axis;

FIGS. 3 and 6 respectively, are fragmentary elevational views in sectionof the flexible tubular member having an end differently formedaccording to the invention;

FIGS. 4 and 7 respectively, are fragmentary elevational views in sectionillustrating an intermediate step in the assembly of differentembodiments of an airspring according to the invention;

FIGS. 5 and 8 respectively, are fragmentary elevational views in sectionillustrating different embodiments of airsprings according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 2, the airspring 10 of the invention is shown in itsinflated condition. The flexible generally tubular member 12 is securedat one end 13 to a plug 16 by means of a ring-shaped fitting 18. Theaxially opposite end 14 of the flexible member 12 is secured to a piston20 by a similar ring-shaped fitting 22. There is formed between the plug16, the piston 20 and the tubular flexible member 12 a sealed chamber 24for containment of the inflation fluid, for example, pressurized air.The flexible member 12 is composed of flexible polymeric material suchas natural or synthetic rubber or other elastomeric material and usuallycontains tension-resisting reinforcements 15 therein. The flexiblemember 12 in its undeformed state, as manufactured (not illustrated) isof a generally cylindrical configuration and typically includes at leastone end portion 30 of tapering thickness (as shown in FIG. 1). Theflexible member 12 as manufactured is of substantially equal thickness(T) throughout its axial dimension and its circumference except for itsends, which may be tapered. The flexible member 12 does not containbeads at its ends.

As used herein, thickness of the member is the shortest distance from achosen point of interest on the outer surface 17 of the flexible memberto the inner-surface of the flexible member 19. Referring to FIG. 2, thethickness (T) of the flexible member 12 is shown at point P which lieson the outer surface of the member.

When used in the airspring 10 of the invention the tapered end portion30 (as illustrated in FIG. 1) of the member 12 is cut off or otherwiseformed in a manner to be hereinafter fully described.

The plug 16 shown is of conventional design and therefore will not befurther discussed.

The piston 20 in an airspring 10 according to the invention includes acircumferentially extending recess 26 adjacent the end 28 of the piston20 which is opposite the part 29 to which the piston 20 is mounted. Inother words, the recess 26 is adjacent the end 28 of the piston whichenters the flexible member 12 upon insertion of the piston 20 into theflexible member 12. The recess 26 is preferably of a depth correspondingapproximately to the thickness of the flexible member 12 with dueallowance for the compression of the flexible member 12 which occursunder load. This allowance may range from about 5 to 20 percent and ispreferably about 10 percent of the thickness of the flexible member 12.It is important that any discontinuity existing in the surface of thepiston 20 and end 25 of the flexible member over which the lobe 23 rollsbe minimal as such discontinuities will alter the spring'scharacteristics and may reduce the life of the flexible member 12.Preferably no discontinuity exists in the surface of the piston 20 andend 25 of the flexible member 12 over which lobe 23 rolls. In theembodiment shown in FIG. 2 the recess 26 is in the configuration of afrustum of a cone. However, this need not be the case. As anotherexample, the recess could be of substantially cylindrical configuration(not shown) depending upon the desired characteristics of the spring.These examples are not intended to limit the invention. When the recess26 is in the configuration of a conical frustum as shown in FIG. 2 it ispreferable that the diameter D of the piston 20 at the end 27 of therecess 26 which is nearest the part 29 to which the piston 20 is mountedbe of a diameter approximately corresponding to the inside diameter (M)of the flexible member as manufactured (refer to FIG. 3 or 6). Suchrelationship between the maximum diameter of the recess and the insidediameter (M) of the flexible member reduces or eliminates flaring of thepiston end 14 of the flexible member 12 outwardly from the piston 20.The end 27 of the recess 26 may be near the end 28 of the piston 20 andimmediate the ring-shaped fitting 22. In a preferred embodiment, similarto that shown in FIG. 2 (see also FIGS. 5 and 8), the end 27 of therecess 26 is distal the end 28 of the piston an amount such that the end14 of the flexible member 12 extends at least three millimeters (oneeighth of an inch) beyond where it is secured to the piston end 28 byring-shaped fitting 22. The cut end 14 of the flexible member 12preferably should not be extended into the working area (WA) of thepiston surface.

The diameter (d) of the end of the piston at the point of attachment ofthe ring-shaped fitting 22 which secures the flexible member 12 to thepiston 20 is preferably of a diameter (d) only slightly smaller thanthat of the inside diameter (M) of the undeformed flexible member 12(refer to FIGS. 2 and 3). Such configuration reduces pull back andflaring of the flexible member 12 from the end 27 of the recess 26 uponattachment of the retaining ring-shaped fitting 22. The outside diameter(d) of the piston at the location of the ring fitting may be from about75 percent to about 95 percent of the inside diameter of the undeformedflexible member 12 and is preferably at least 90 percent of the insidediameter of the undeformed flexible member 12 and most preferably isabout 95 percent of the inside diameter of the undeformed flexiblemember 12.

Referring to FIG. 1 there is shown an airspring 50 according to theprior art. In such an assembly it is common for the tapered end portion30 of the flexible member 12 to extend down into the working area (WA)of the surface of the piston 52. As a result the tapered end portion 30adds to the circumference of the piston 52 thus changing the airspring'sfine tuned characteristics. Because both the thickness and the length ofthe tapered end portion 30 extending into the working area (WA) of thepiston surface can vary from one assembly to another, it is difficult,if not impossible, to allow for the contribution of tapered end portion30 to the piston's 52 overall dimensions. As used herein, the workingarea (WA) is that area of the piston surface over which the rolling lobe23 of the flexible member 12 travels and resides during a majority ofthe airspring's operation when operated in accordance with designinflation, load and input variations.

One preferred method of assembly of the airspring 10 of the inventionbegins by co-axially aligning the piston 20 with the flexible member 12and then inserting the end 28 of the piston 20 into the member 12 sothat the tapered portion end (not shown in FIG. 2 but similar to portion30 of FIG. 1) of the member 12 extends beyond the end 27 of the recess26 and over at least part of the working area of the piston 20. Theflexible member 12 is then secured to the end of the piston 20 as by aring-shaped fitting 22 which, by way of example only, may be acompression ring or a swaged ring. Such rings are typically of a metalcomposition, for example, brass or aluminum. The tapered end portion 30of the flexible member 12 is then trimmed off at a point correspondingto the end 27 of the recess 26 which is distal the piston ring-shapedfitting 22 so that the member 12 substantially fills the recess 26.

The trimming operation (not illustrated) is conveniently done with alathe. The piston 20 with the flexible member 12 secured thereto ischucked into the lathe and the excess of the flexible member 12including its tapered end portion 30 is cut away at a pointcorresponding to the end 27 of the recess 26 which is distal the pistonring-shaped fitting 22.

The flexible member may have its tapered end portion 30 cut off prior toinsertion of the piston into the flexible member; however, in thisinstance application of the retaining ring-shaped fitting 22 to securethe flexible member 12 to the piston 20 may result in pull back of thecut end 25 of the flexible member from the end 27 of the recess 26 whichis distant from the piston ring-shaped fitting 22 if allowance is notmade for this phenomenon. The resulting gap (not shown) between the end25 of the member 12 and the end 27 of the recess 26 is undesirable sincein operation when full rebound of the airspring occurs the rolling lobe23 must pass over the recessed area of the piston 20. As discussedpreviously herein, such discontinuities are undesirable.

According to the invention, another method of avoiding or minimizing anygap between the trimmed end 40 of the flexible member 12 and the end 27of the recess 26 is illustrated in FIGS. 3-5. Referring to FIG. 3, thetapered end portion 30 of the flexible member has been trimmed away atan angle less than ninety (90) degrees to the longitudinal axis (1a) ofthe flexible member 12 so as to form an inside chamfer 41. The includedangle (α) of the sides of the chamfer 41 is, of course, less than onehundred eighty (180) degrees, and preferably ranges from about 170 to 90degrees and, most preferably from about 170 to 130 degrees. Of course,the flexible member 12 could be formed, as by molding, with such achamfered end. After trimming away of the end of the flexible member toform an end 40 having an inside chamfer 41 as shown in FIG. 3, thechamfered end 40 of the flexible member 12 is coaxially aligned with andpositioned over the end of the piston 20 such that a predeterminedamount of the flexible member 12 extends beyond the end 27 of the recess26 which is distal the end 28 of the piston 20 to which the flexiblemember 12 is secured. This amount, shown as distance x in FIG. 4, ischosen so that when the ring-shaped fitting 22 is applied, the chamferedend 40 of the flexible member 12 is thereby pulled back toward thering-shaped fitting 22 and drops into the recess 26 without leaving anysubstantial gap. The clamping action of the ring-shaped fitting 22,particularly when a swaged ring is employed, causes the acutely pointedtip 42 of the chamfered end 40 of the flexible member 12 to be drawntoward the ring-shaped fitting 22 a greater amount than the obtuselyangled radially inner tip 43 of the chamfered end 40 of the flexiblemember 12. Upon application of the ring-shaped fitting 22 the chamferedend 40 of the flexible member 12 flares slightly radially outwardly andat the same time is drawn toward the ring-shaped fitting 22, thusallowing the chamfered end 40 to drop into and substantially fill therecess 26.

According to the invention, yet another method of assembling a flexiblemember 12 having a preformed or pre-trimmed end to the piston withoutany substantial gap is shown in FIGS. 6-8. As shown in FIG. 6, the end62 of the flexible member 12 which is to be secured to the piston 60 isfirst formed, as by trimming or molding, for example, substantiallysquare, that is, at an angle (k) of about ninety (90) degrees relativeto the longitudinal axis (1a) of the undeformed flexible member 12. Asshown in FIG. 7, the square-formed end 62 of the flexible member 12 isthen coaxially aligned with and positioned over the end of the piston 60a predetermined amount such that the end of the flexible member 12extends beyond the end 64 of the recess 63 a predetermined amount (y).Upon application of the ring-shaped fitting 22, particularly when aswaged ring is employed, the square cut leading edge 66 of the flexiblemember 12 is drawn back toward the ring-shaped fitting 22 and seatsalong the base 67 of the recess 63. As in the assembly of FIG. 5, theouter surface 17 of the flexible member is drawn toward the ring-shapedfitting a greater amount than the inner surface 19 of the flexiblemember 12. The approximately perpendicularly formed end of the flexiblemember 12 drops into and substantially fills the recess 63 uponapplication of the ring-shaped fitting 22. Note that the end of therecess is not perpendicular to the longitudinal axis or axial centerlineof the piston as in the embodiment of FIGS. 2 and 5, but rather, is atangle (b), which preferably is from about 85 to 65 degrees relative tothe longitudinal axis of the piston.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention it will be apparent to thoseskilled in the art that various changes and modifications may be madetherein without departing from the spirit or the scope of the invention.

We claim:
 1. A rolling lobe fluid spring comprising:a mounting member; apiston having a radially extending mounting end, and an axially andcircumferentially extending piston surface, the surface includingcircumferentially extending serrations axially adjacent the pistonmounting end, a circumferentially extending working area axially awayfrom the piston mounting end and serrations, and a circumferentiallyextending recess extending axially between the serrations and theworking area, the recess having a circumferentially extending blunt endaxially adjacent the working area and axially away from the mounting endand serrations; and a flexible, tubular member having a first end and asecond end with a leading edge, the tubular member being ofsubstantially uniform thickness throughout the second end to the leadingedge, such that the second end is a taper free, blunt end, and theleading edge is a blunt leading edge, the first end of the tubularmember being mounted and secured in a fluid tight manner to the mountingmember, and the second end of the tubular member being mounted andsecured to the piston in a fluid tight manner about the serrations, (a)such that a circumferentially extending area of securement is defined inthe second end of the tubular member, (b) such that a rolling lobe isformed in the tubular member between the area of securement and thefirst end of the tubular member which extends longitudinally, past thepiston recess to the working area, and (c) such that the non-tapered,blunt tail including the blunt leading edge is formed in the second endof the tubular member; the blunt tail extending from the securement areain a direction within the tubular member away from the rolling lobe andfirst end; the blunt tail being in the recess and thereby being betweenthe rolling lobe and piston; and the blunt tail substantially fillingthe recess both axially and radially such that the blunt leading edge ofthe tail lies at the blunt end of the recess without a substantial gapbetween the blunt leading edge and blunt end of the recess, and furthersuch that the tail has a radially outer surface which, with the workingarea, presents a substantially continuous surface over which the rollinglobe may roll.
 2. A rolling lobe fluid spring as in claim 1 in which therecess of the piston surface is frustoconical, and in which the blunttail at the blunt leading edge of the tubular member is substantiallytension free, whereby the blunt tail does not flare outwardly from thepiston.
 3. A rolling lobe fluid spring as in claim 1 further comprisinga ring fitting which mounts and secures the tubular member to the pistonin the area of securement, and in which the ring fitting compresses thetubular member in the area of securement by a diametric amount in therange of about 5 percent to about 25 percent.